Alloys consisting of a plurality of metal elements exhibit properties different from those of component metal elements. Therefore, unique properties that were not able to be attained with conventional metals are expected to be obtained by creating a new alloy. On the other hand, metal fine particles such as metal nanoparticles have a large surface area and can exhibit properties and structures different from bulk materials, and therefore are expected to be used in various applications. For these reasons, a variety of alloy fine particles have been previously studied. Also, in the application of an exhaust gas purifying catalyst for an automobile, use of such alloy fine particles as a catalyst component has been investigated.
Japanese Unexamined Patent Publication (Kokai) No. 2006-198490 describes an exhaust gas purifying catalyst comprising a support consisting of an oxide and alloy particles supported on the support wherein the alloy particles are a solid solution of a plurality of metal components, wherein the alloy particles have a particle diameter of 100 nm or less, and wherein the alloy particles are a solid solution of at least two of Pt, Ir, Pd, Rh, Ru, Au and Ag.
Japanese Unexamined Patent Publication (Kokai) No. 2010-194384 describes a catalyst for purification of exhaust gas comprising a support made of a metal oxide; and metal particles supported on the support, wherein the metal particles are made of a solid solution of at least one first metal selected from the group consisting of Pt, Ag, Mn, Fe and Au with at least one second metal selected from the group consisting of Pd, Rh, Ir and Ru, an average primary particle diameter of the metal particles is 1.5 nm or less, and a standard deviation in metal composition ratio of each primary particle of the metal particles is 10% or less.
Japanese Unexamined Patent Publication (Kokai) No. 2005-313012 describes an exhaust gas purifying catalyst comprising a substrate and catalytic active particles wherein the catalytic active particles are dispersed and supported on the substrate and are shaped into a shell form from one or more metals or metal oxides, wherein the catalytic active particles have a diameter in a longitudinal direction of 5 nm to 20 nm and a thickness is 1 nm to 10 nm, and wherein the catalytic active particles are formed by one or more metal elements selected from Pt, Rh, Pd, Au, Ag and Ru; a solid solution comprising two or more of the metal elements; or a metal oxide obtained by oxidizing the metal elements.